1. Field of the Invention
The invention relates to a sheet feeding apparatus and an image forming apparatus, and particularly to a sheet feeding apparatus having detachably mounted thereon a feed roller for feeding a sheet.
2. Description of the Related Art
Heretofore, in an image forming apparatus such as a printer, a copying machine or a facsimile apparatus, there has been provided a sheet feeding apparatus for separating and feeding out sheets one by one from sheet stacking means on which a plurality of sheets are stacked.
FIG. 12 illustrates the construction of such a conventional sheet feeding apparatus, and in FIG. 12, the reference numeral 70 designates a sheet feeding cassette, the reference numeral 1 denotes a feed roller for feeding sheets P contained in the sheet feeding cassette 70, and the reference numeral 72 designates a cassette tub which is the frame member of the sheet feeding cassette 70. The reference numeral 73 denotes an inner plate provided for pivotal movement in a vertical direction in the cassette tub 72, and the reference numeral 74 designates an inner plate urging spring for urging the inner plate 73 toward the feed roller 1, and the inner plate 73 is urged toward the feed roller 1 by this inner plate urging spring 74. The sheets P stacked on the inner plate 73 are successively fed out by the rotation of the feed roller 1. The reference numeral 76 denotes a separation pad brought into pressure contact with the feed roller 1 to thereby separate the sheets fed out one by one.
The feed roller 1 is provided with a sheet abutment portion 1a formed of a frictional material such as frictional rubber, and having a shape in which a part of the circumferential portion is cut away, and rotatable members 3 disposed on the opposite sides of this sheet abutment portion 1a. In a standby state before the sheet P is fed out, the cut-away portion of the sheet abutment portion 1a faces the sheet P, as shown in FIG. 12. When in this state, the sheet P is adapted to abut against the rotatable members 3.
When in this state, the feed roller 1 is rotated, the sheet abutment portion 1a abuts against the sheet P, and by the utilization of the frictional force of the sheet abutment portion 1a, the uppermost one P1 of the sheets P stacked on the sheet feeding cassette 70 is fed out to an image forming portion. If a plurality of sheets are about to be fed at a time, they are separated by the separation pad 76 and only the uppermost sheet is fed.
Now, in the conventional sheet feeding apparatus of such a construction, when the frictional rubber (of the sheet abutment portion 1a) of the feed roller 1 is deteriorated by abrasion or the like, a reduction in feeding performance may be caused. Therefore, design is made such that the feed roller 1 can be detachably mounted on the main body of the sheet feeding apparatus so that the feed roller 1 can be periodically interchanged.
Here, as described in Japanese Patent Application Laid-open No. 2004-256287, there is a sheet feeding apparatus in which a feed roller is made into a unit to facilitate the interchanging work of the feed roller by a user or a serviceman, and is adapted to be slid along the axis of the feed roller and detached from the main body of the apparatus.
FIGS. 13 and 14 show the construction of such a feed roller made into a unit. This feed roller 1 has a roller body portion 1A provided with a sheet abutment portion 1a formed of cylindrical frictional rubber, and a core metal 1b having the sheet abutment portion 1a secured to the central portion thereof. Further, a convex fitting portion 1c is formed on one end portion of the core metal 1b of this roller body portion 1A, and a concave fitting portion 1d is formed on the other end portion thereof.
Cylindrical urging means 5 such as, for example, a coil spring, is inserted into the concave fitting portion 1d, whereafter a shaft member 2 constituting a first roller shaft provided on one side of the roller body portion 1A is slidably inserted thereinto.
Also, a resilient restraining claw 1e for restraining a first rotatable member 3a mounted on the shaft member 2 is provided in the concave fitting portion 1d which is a shaft holding portion for slidably holding the shaft member 2. The first rotatable member 3a is mounted through this resilient restraining claw 1e, whereby the shaft member 2 is slidably held on the roller body portion 1A.
Accordingly, the shaft member 2 is held in an outwardly urged state on the roller body portion 1A by the compressed urging means 5. At this time, the urging means 5 can be further compressed, whereby when the distal end of the shaft member 2 is fixed, the roller body portion 1A can be slid to the distal end side of the shaft member 2.
On the other hand, as shown in FIG. 14, the convex fitting portion 1c provided on one end portion of the core metal 1b constitutes a second roller shaft, and an engagement groove 1g formed in the distal end portion is adapted to be fitted to a drive input shaft 6 provided on the main body of the sheet feeding apparatus. Thus, the feed roller 1 is also adapted to be rotated with the rotation of the drive input shaft 6. The reference character 3b designates a second rotatable member rotatably restrained on the roller body portion 1A.
FIGS. 15A and 15B show a state in which the feed roller 1 thus made into a unit is rotatably held by a holder 10 which is a holding portion provided in the sheet feeding apparatus. In FIGS. 15A and 15B, the reference characters 4a and 4b denote first and second bearings, respectively, detachably held on the holder 10 by a resilient restraining claw or the like, not shown, and constituting first and second journalling portions, and the feed roller 1 is rotatably and resiliently held on the holder 10 through the first and second bearings 4a and 4b. 
When the feed roller 1 is to be detached, the sheet feeding cassette 70 is first detached, whereafter as shown in FIGS. 16A and 16B, the roller body portion 1A is slid in a detaching direction indicated by the arrow along the first roller shaft 2. Thereby, the convex fitting portion 1c which is the second roller shaft is moved with integrally with the roller body portion 1A and comes off from the fitting with the second bearing 4b, and as shown in FIG. 16B, the feed roller 1 becomes capable of being tilted as indicated by the arrow.
As the result, the feed roller 1 can be detached as shown in FIG. 17. Also, when the feed roller 1 is to be mounted, it can be mounted by a converse procedure. As described above, the interchange of the feed roller 1 can be performed easily.
On the other hand, as another example of the sheet separating means carried on the sheet feeding apparatus, there is one using a separation roller having a torque limiter disposed coaxially therewith or containing a torque limiter therein. This separation roller is adapted to be brought into pressure contact with the feed roller, and separate the sheet by the braking torque of the torque limiter.
For example, when a plurality of sheets are present between the feed roller and the separation roller, relatively small rotational torque acts on the torque limiter and therefore, the torque limiter is adapted to block the rotation of the separation roller associated with the rotation of the feed roller. Thereby, a single sheet can be conveyed by a conveying roller, and other sheets can be prevented from being conveyed by the separation roller.
When only one sheet is present between the feed roller and the separation roller, great rotational torque acts on the torque limiter, and the torque limiter permits the rotation of the separation roller associated with the rotation of the feed roller. Thereby, the sheet is conveyed.
FIG. 18 shows the construction of a conventional sheet feeding apparatus in which the sheet is separated by a separation roller using such a torque limiter.
In FIG. 18, the reference numeral 11 designates a cylindrical feed roller free of a cut-away portion, and the reference numeral 62 denotes a separation roller, and a torque limiter 62a is provided coaxially with this separation roller 62. The reference numeral 63 designates a separation roller holder for supporting the separation roller 62 for sliding in a vertical direction, and the reference numeral 64 denotes a spring for urging the separation roller 62 toward the feed roller 11.
The separation roller 62 is brought into pressure contact with the separation roller holder 63 interposed therebetween by the spring 64, whereby a sheet P fed out by the feed roller 11 is separated by the braking torque of the torque limiter of the separation roller 62, and is conveyed toward the downstream.
FIG. 19 is an exploded perspective view of the feed roller 11, and in FIG. 19, the reference character 11A designates a roller body portion, the reference character 11a denotes a sheet abutment portion (e.g. a rubber material), the reference character 11c designates a convex fitting portion (second roller shaft), the reference character 11d denotes a concave fitting portion, and the reference character 11e designates a resilient restraining claw. The reference character 11f denotes a flange portion, the reference character 11g designates an engagement groove engaged with a drive input shaft, the reference numeral 12 denotes a shaft member constituting a first roller shaft, and the reference numeral 15 designates urging means such as a coil spring for outwardly urging the shaft member (first roller shaft). The functions of these members and the like are the same as the function of the feed roller used in combination with the separation pad already described and therefore need not be described.
The reference numeral 13 denotes an auxiliary cap for slidably supporting the shaft member 12 on the roller body portion 11A, like the first rotatable member 3a in the feed roller used in combination with the separation pad.
This feed roller 11, like the feed roller 1 used in combination with the separation pad shown in FIG. 13 already described, is such that the roller body portion 11A is slidably held along the first roller shaft (shaft member 12). Again in this feed roller 11, as shown in FIG. 20, the roller body portion 11A is slid in the direction indicated by the arrow, whereby the feed roller 11 can be interchanged easily by the user or the serviceman.
However, in the conventional sheet feeding apparatus and image forming apparatus wherein the feed roller is thus detachably mounted and is made interchangeable, there are the following problems.
(1) In a case where a sheet has been jammed between the feed roller and the sheet separating means (the separation pad or the separation roller), when the jam is to be cleared, the feed roller may be inadvertently detached.
This is because there is the possibility of vehement bend or breakage occurring to the jammed sheet, and there is the possibility that the user (or the serviceman) may perforce pull the sheet thus causing vehement bend or breakage during the clearance of the jam. Particularly, in a case where the clearance of the jam is done without the sheet feeding cassette being detached from the apparatus, that is, without the abutment between the feed roller and the sheet separating means being released, the bend or slack of the jammed sheet may be caught by the end portions of the feed roller to thereby slide the feed roller.
(2) In a case where the mounting direction of the sheet feeding cassette is the same as the sliding direction of the feed roller, when jam has occurred with a sheet nipped between the feed roller and the sheet separating means, if the sheet feeding cassette is drawn out, there is the possibility of the jammed sheet sliding the feed roller.
(3) There is the possibility that an unexpected great force may be applied to the feed roller during the transportation of the apparatus to thereby detach the feed roller.
In a case where the feed roller has been inadvertently detached under such situations as noted above, if the user can become aware of this, the feed roller can be re-mounted easily, but if the user does not become aware of this, he will judge it to be trouble of the apparatus.
If here, a sensor for exclusive use is provided so as to detect the mounted state of the feed roller, it will result in a high cost. Also, if the urging force (spring force) of the urging means contained in the feed roller is strengthened so that the feed roller may not be detached, the interchanging work of the feed roller will become difficult.
So, it is conceivable to provide a locking member to prevent the feed roller from being inadvertently detached. In a case where the locking member is thus provided, when the feed roller is to be interchanged, the locking member is changed over a lock position to a lock releasing position, whereafter the feed roller is interchanged. Also, design is made such that after the interchange of the feed roller, the locking member is changed over from the lock releasing position to the lock position.
However, if the locking member is thus provided, there will be a case where after the interchange of the feed roller, the user forgets to change over the locking member to the lock position. In such case, when the sheet feeding cassette is to be mounted thereafter, the locking member may sometimes contact with the sheets stacked on the sheet feeding cassette, and when the locking member thus contacts with the sheets, there will occur the inconvenience that the feeding of the sheets at appropriate timing is not performed, or the sheets are injured.